What is the recommended dose and duration of Keflex (Cephalexin) for a 13-year-old patient weighing 44.8 kg with preseptal cellulitis?

Cephalexin (Keflex) Dosing for Preseptal Cellulitis in a 13-Year-Old

For this 13-year-old patient weighing 44.8 kg with preseptal cellulitis, administer cephalexin 500 mg orally every 12 hours for 10 days.

Dosing Rationale

Weight-Based Calculation

• The FDA-approved pediatric dosing for cephalexin is 25-50 mg/kg/day in divided doses for skin and skin structure infections 1
• For this 44.8 kg patient, the standard dose range would be 1,120-2,240 mg/day 1
• The recommended regimen of 500 mg every 12 hours (1,000 mg/day total) falls appropriately within this range and aligns with FDA guidance for patients over 15 years of age with skin infections 1

Age-Appropriate Dosing Considerations

• Since this patient is 13 years old and weighs 44.8 kg (close to the 40 kg threshold), they can receive the adult dosing regimen of 500 mg every 12 hours 1
• The FDA specifically states that for skin and skin structure infections, 500 mg may be administered every 12 hours 1
• This twice-daily dosing improves adherence compared to four-times-daily regimens 2

Treatment Duration

The treatment duration should be 10 days for preseptal cellulitis 1

• The FDA label specifies that for β-hemolytic streptococcal infections (a common cause of preseptal cellulitis), cephalexin should be administered for at least 10 days 1
• Recent pediatric studies of preseptal cellulitis demonstrate successful outcomes with 7-10 day courses, with most patients showing improvement within 48-72 hours 3, 4

Clinical Monitoring

Expected Response Timeline

• Clinical improvement should be evident within 48-72 hours of initiating therapy 2
• If no improvement occurs within this timeframe, reevaluation is necessary to assess for complications such as orbital extension or abscess formation 4

Warning Signs Requiring Escalation

• Development of proptosis, chemosis, ophthalmoplegia, or vision changes would indicate progression to orbital cellulitis requiring hospitalization and IV antibiotics 4
• Persistent fever beyond 48-72 hours or worsening eyelid swelling warrants imaging (CT scan) and possible antibiotic change 3, 4

Important Clinical Considerations

Common Pitfalls to Avoid

• Do not underdose: While 250 mg every 6 hours is an alternative FDA-approved regimen, the 500 mg every 12 hours dosing provides better adherence and adequate coverage 1
• Complete the full 10-day course even if symptoms improve earlier, particularly given the streptococcal coverage requirement 1

Alternative Considerations for Treatment Failure

• If the patient fails to respond to cephalexin within 48-72 hours, consider MRSA coverage with clindamycin 10-13 mg/kg/dose (approximately 450 mg) every 8 hours, as recent studies show clindamycin is commonly used for preseptal cellulitis 3
• Imaging with CT scan should be obtained if orbital cellulitis is suspected based on clinical deterioration 4

Formulation Selection

• For a 13-year-old, capsules or tablets are preferred over suspension 1
• If suspension is necessary, use the 250 mg/5 mL concentration: administer 10 mL (2 teaspoons) every 12 hours 1